1. Field of the Invention
The invention relates to an axial flux induction motor comprising a stator having poles and a rotor facing the stator, which rotor comprises a first part of a first material and second part of a second material, which first material has a relatively high permeability compared with the second material and which second material has a relatively high electrical conductivity compared with the first material, which first part is disk-shaped and has a first outer radius R.sub.1, which second part is disk-shaped and has a second outer radius R.sub.2 and comprises at least a portion which extends between the stator and the first part.
The invention also relates to a vacuum cleaner comprising an impeller wheel driven by such an axial induction motor.
2. Description of the Related Art
Such an induction motor is known, for example, from EP 0 487 141 A2. This known motor forms part of a fan unit for generating gas streams, particularly for vacuum cleaners, and comprises an impeller wheel which is also electromagnetically active and in conjunction with electromagnetically active parts of the motor stator generates the torque of the impeller wheel. The electromagnetically active part of the impeller wheel is a conductive disc which is arranged in a radial plane opposite the stator and bounds the radial air gap at the rotor side. The electrically conductive rotor disc is, for example, a basic disc of the impeller wheel and is made of, for example, aluminium. At its side which is remote from the air gap this electrically conductive basic rotor disc is backed with a disc of a high-permeability material, i.e. a magnetically highly conductive layer, for example of solid iron. The known motor has the disadvantage that the rotor breaks down at a certain circumferential rotation speed due to centrifugal forces.